Type 'donate my eggs' into a search engine and 43,000 sites come up; many of them are noticeboards for American college girls offering their eggs for sale in the US, where this is legal in some states ($4,000-$6,000 can go a long way towards college fees). There are very few women - though there are some - offering their eggs for nothing.

There are various reasons for electing to use another woman's eggs. Some women are unable to produce eggs, others may have ovarian failure due to early menopause or because surgery or chemotherapy have made them sterile. Also, some genetic disorders can be passed on through the mother's egg and women may opt to use another woman's eggs to prevent this. And, as described above, older women may have a better chance of having a baby if they use eggs from a younger woman.

In the UK, with the Human Fertilisation and Embryology Authority's ban on the sale of eggs, women who have opted for this route must rely on donated eggs. 'There is an acute shortage of egg donors in the UK, which causes heartache for hundreds of women unable to conceive a child,' says Fiona Stirling from the National Gamete Donation Trust, a charity which raises awareness of the need for donors, and supports potential donors.

According to the HFEA, in the year ending March 2001, there were approximately 24,000 IVF cycles. Of these, 1,783 used donated eggs and 190 donated embryos. There were 465 live births resulting from both the donated eggs and embryos. There are no figures on how many eggs were donated anonymously but the figure is low.

Kriss Fearon is 36 years old and has donated eggs anonymously on three separate occasions. One child has been born as a result. 'I became a donor hoping that I would be able to help a couple suffering the pain of infertility to fulfil their wish to have a child. It's as simple as that,' she says.

'I'd seen people go through that trauma, read about egg donation and eventually decided I would do it. For a long time I didn't want children of my own so I was prepared for the risks, and I wanted to do something positive with my fertility. It was going to waste every month, and there were people suffering who could use my eggs. I wanted to do something constructive, to feel useful. The benefit for me was to feel like a better person for having helped someone in need.'

The chances of getting pregnant using donated eggs varies according to the woman's age and biological factors. The success rate for IVF in general is about 20-27 per cent, though some clinics do experience success rates of almost 50 per cent.

Potential donors must be between 18 and 35 years old, under 85kg and not have had epilepsy, diabetes or any other serious infection such as HIV, hepatitis B or C. The procedure for egg donation is much the same as that for a woman undergoing IVF treatment. The ovaries need to be suppressed by either daily nasal sprays or injections for about four weeks. They are then stimulated with daily injections for a further 10 days. On top of this there are regular ultrasound scans and blood tests. The egg collection is generally carried out under general anaesthetic.

The HFEA is keen to stress that the procedure is not without risk. Hot flushes, headaches and sleeplessness are some of the potential side-effects. More serious if less common risks include ovarian hyper-stimulation syndrome which causes fluid retention, abdominal discomfort, nausea and vomiting. There is also concern among some clinicians about the long-term impact of over-stimulating the ovaries and an increased risk of ovarian cancer.

Kriss Fearon has had no contact with the recipients of her eggs, but although she now has concerns about the impact on the child of not being allowed access to information about her, she does not regret it. 'I had the normal worries common to women becoming donors. Things like, will it hurt, will it affect my own fertility, what kind of side-effects will the drugs have,' she says. 'But I'm proud of being a donor. It's something in my life that I think I've done right.'